Lymphatic leukemias are induced in normal and immunodeficient mice using viruses and chemical agents. These neoplasms are characterized histologically and T or B lymphocyte origin is identified using immunologic techniques. Bibliographic references: Fieldsteel, A.H., Kurahara, C., and Dawson, P. Helper specificity for retrieval of defective Friend virus. Int. J. Cancer 15: 522-527, 1975. Dawson, P.J., and Fieldsteel, A.H. Protection of A/He virus by a Friend virus pseudotype against challenge with Friend virus. Proc. Soc. Exp. Biol. Med. 149: 61-63, 1975.